Low permeability airbag and method

ABSTRACT

An airbag having low gas permeability characteristics. The airbag is formed from two separate layers of material, an inner layer having low air permeability and an outer strength layer enclosing the inner layer, where the layers are only attached together along seam lines. The inner layer is made from a film material, preferably urethane. The outer layer is formed from a fabric.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to low permeability airbags. Morespecifically, the present invention relates to airbags that are requiredto stay inflated for extended periods of time in order to protectoccupants in a vehicle in the event of a sustained collision event, suchas a rollover. An example of such an airbag is a side curtain airbag.

[0002] Traditional airbags are manufactured by means of sewing panels offabric together to form a substantially enclosed, three dimensional bag,where the only substantial opening in the bag (other than vents) isdesigned to receive the inflator means. Typically, airbags are made fromwoven fabrics, and bags of desired shape have been produced by sewingpanels of various shapes and dimensions. Sewn seams may be adequate forsome driver and passenger applications because the required time for gasretention on these bags is less than one second.

[0003] This manufacturing method is unsuitable for side curtain airbags,and the like, because the holes created in the fabric by the sewingprocess allow gas to leak out, which reduces the gas retention time tounacceptable levels. Further, in order to obtain fabrics having low airpermeability, it has generally been necessary to apply a heavy coatingor lamination to the fabric, which is a costly step in the manufacturingprocess.

[0004] One solution that has been proposed to address this leakage issueis to attach the fabric panels together through welding means. Whilethis method may prevent or reduce leakage at the seams, the fabric muststill be heavily coated or laminated, and it has proven difficult toweld fabric directly to fabric.

[0005] Thus, it would be desirable to provide an airbag having low airpermeability, which would not allow significant gas leakage at the seamsthereof, and which would not require a minimal amount of lamination orcoating on the face of the airbag fabric or substrate.

OBJECTS OF THE INVENTION

[0006] Accordingly, it is an object of the present invention to providea low permeability airbag cushion that prevents or reduces leakage alongthe seams thereof.

[0007] Another object of the present invention is to provide a low gaspermeability airbag cushion that reduces the use of costly laminates andcoatings that must be applied to a face of the airbag fabric.

[0008] Yet another object of the present invention is to provide a lowgas permeability airbag cushion having an inner bag enclosed in an outerbag, thus forming a double-layered airbag cushion.

[0009] Yet another object of the present invention is to provide a lowcost fabric or non-woven on the outside, but having a low permeabilityinner cushion. The fabric component functions primarily as a strengthprovider rather than as a means to impart low permeability.

[0010] Another object of the present invention is to provide an innerbag enclosed in an outer bag, thus forming a double-layered airbagcushion that could be used on the driver, passenger, or side airbagapplications.

[0011] Still another object of the present invention is to provide amethod for producing a low gas permeable airbag, wherein the processprevents the airbag from being punctured in such a way that would allowleakage along the seams thereof.

[0012] Another object of the present invention is to provide aninexpensive airbag cushion and method for manufacturing such an airbagcushion, which minimizes or eliminates the use of expensive coatings andlaminates, and which addresses other problems associated with themanufacture and production of airbag cushions having low gaspermeability characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

[0014]FIG. 1 shows a driver side airbag made in accordance with thepresent invention;

[0015]FIG. 1A shows a side curtain airbag made in accordance with thepresent invention;

[0016]FIG. 2 shows a cross sectional cut-out portion of an airbag madein accordance with the present invention, illustrating the two innerlayers of film sandwiched between the two outer layers of fabric,wherein the air pocket is formed within the film layers, creating anairbag having an inner film layer and an outer fabric layer;

[0017]FIG. 3 shows a cross section of a heat welded seam, where the fourlayers of shown in FIG. 2 are heat welded together, and a seam is sewnthrough the four layers along and through the polymeric bead formed bythe heat welding process;

[0018]FIG. 3A shows a cross section of an alternate embodiment of theinvention, where the inner film layers are heat welded together, and theouter layers are sewn together, so that the resulting inner film layeris disposed within the resulting outer fabric layer, without beingattached directly thereto;

[0019]FIG. 3B shows a side airbag curtain having inflation controlareas, where the perimeter of the outer layer is sewn only through theouter layers, as shown in FIG. 3A, and where the inner film layers areheat welded together to form inflation control areas, and furthershowing a sewn seam positioned within the inflation control areasattaching the outer layers to the inner layers.

DETAILED DESCRIPTION

[0020]FIG. 1 shows a driver side airbag 2 having low gas permeabilitycharacteristics. The airbag is formed from two separate layers ofmaterial, an inner layer and an outer layer enclosing the inner layer,where the layers are only attached together along seam lines. The innerlayer is preferably made from a film material, more preferably urethane,and is primarily used to provide a low air permeability layer to theairbag. The outer layer is preferably formed from a fabric, and servesprimarily to enhance the strength characteristics of the airbag. FIG. 1Ashows a side curtain airbag 4, which may be formed similarly from aninner film layer and an outer fabric layer.

[0021] In a first method, the instant airbag is manufactured by stackingtwo separate layers of film 6 material between two separate layers offabric material 8, as shown in FIG. 2. The two layers of film may beformed from two separate sheets (as shown), or may be formed from asingle sheet folded over. Similarly, the two layers of fabric may beformed from two separate sheets (as shown), or may be formed from asingle sheet folded over with the two layers of film stacked therebetween. The layers are then subjected to heat welding, or some othersuitable attachment procedure, which forms the shape and the innerchambers of the bag. As used herein, the term “heat welding” means anymethod of sealing the layers of the airbag cushion together, which formsa polymeric bead or fused polymeric seal, including but not limited tosuch methods as radio-frequency bonding, ultrasonic bonding, inductionwelding, adhesive bonding, etc. In a preferred embodiment, the heatwelding produces either a pair of polymeric beads spaced slightly apartor a continuous thick bead 10, forming the seams of the airbag cushion.

[0022] The polymeric bead 10 produced by the heat weld seals all fourlayers together, which results in the formation of a film bag within afabric bag. Optionally, a stitched seam 12 may be sewn within theboundaries of each heat-welded seam through the polymeric bead 10, asshown in FIG. 3, in order to provide more strength. The stitched seam 12may be applied either before the heat welding of the bag or after theheat welding of the bag. Because the stitching occurs within thepolymeric bead 10 as shown, the holes punched in the bag as a result ofthis stitching do not allow gas to leak from the bag when the bag isinflated.

[0023] This arrangement allows the film bag to retain the gas when thebag is inflated, and prevents leakage through sewn seam holes, becausenone of the holes produced by the stitching step are produced on aninflated portion of the bag. The holes are only produced between orwithin the polymeric beads of the heat weld. The outer layer of fabricprovides strength, and is only attached to the inner bag along thesealed seams thereof. The non-heat welded portions of the bags are notattached to each other, in the first embodiment.

[0024] Tests have been performed with a welded polyurethane film bag ina 420 d uncoated fabric bag. The development sample was inflated to apeak pressure of 14 Psi, and the leak rate was measured. After 40minutes, the bag pressured had dropped by about 0.6 Psi.

[0025] In a second method for manufacturing the instant airbag cushion,two layers of the film material are stacked, one layer on top of theother layer. As before, these layers may be formed from a single sheetfolded over or two separate sheets. The two layers of film material arethen heat sealed together to form a film bag. Then, the outer bag may bepositioned to encompass the inner bag by stitching the outer bag outsidethe polymeric beads formed on the seams of the inner bag at theperimeter, as shown in FIG. 3A, and attached to the inner bag bystitching in-between or outside the polymeric beads in the inflationcontrol areas 14 (other than perimeter seams) as shown in FIG. 3B. Sucha side airbag may also include discrete vents (not shown) in the bag forenergy dissipation.

[0026] In this method of manufacture, the outer bag is only connected tothe inner bag by a stitched seam, and is not attached to the inner bagby means of heat welding. The outer bag may either be assembled onto theinner bag by stitching individual panels separately (or simultaneously)to the seams of the inner bag, or the outer bag may be assembled firstwith a small opening, and the inner bag may then be positioned withinthe pre-assembled outer bag for attachment thereto.

[0027] The sewn seam at the weld interface helps to transfer the stressaway from the polymeric bead to the fabric, thus strengthening theairtight seam against gas leakage. The polymeric bead still retains itselongation properties after the weld is cooled, which helps to maintainthe airtight structure. Although stitching has been set forth as thepreferred method for attaching the outer bag to the inner bag in thesecond embodiment, it should be understood that other methods ofattachment may be employed, including but not limited to suitablemethods of bonding, adhesive, etc.

[0028] It should be understood that other film materials may be used,including but not limited to polyester, polyamides, polyolefin, etc.Similarly, other fabrics may be employed for the outer bag, includingbut not limited to woven, non-woven, weft-insertion, etc.,

[0029] Although the present invention has been described in considerabledetail with reference to certain preferred versions thereof, otherversions are possible. Therefore, the spirit and scope of the appendedclaims should not be limited to the description of the preferredversions contained herein.

What is claimed is:
 1. A airbag cushion comprising: a substantiallyenclosed inner bag made of a first material; and an outer bag made ofsecond material, said outer bag being attached to and enclosing saidinner bag.
 2. The airbag cushion set forth in claim 1, wherein saidinner bag includes at least one seam, where opposed portions of saidfirst material are attached together to form a substantially enclosedbag.
 3. The airbag cushion set forth in claim 2, wherein said outer bagis attached to said inner bag along said seam.
 4. The airbag cushion setforth in claim 2, wherein said seam comprises at least one polymericbead.
 5. The airbag cushion set forth in claim 2, wherein said outer bagis sewn to said inner bag within the boundaries of said seam on saidinner bag.
 6. The airbag cushion set forth in claim 1, wherein saidinner bag is made from material selected from the group consisting ofurethane, polyamide, polyester, silicone, polyolefin, and anycombinations thereof
 7. The airbag cushion set forth in claim 1, whereinsaid outer bag is made from material selected from the group consistingof woven fabric, non-woven, film and any combinations thereof.
 8. Theairbag cushion set forth in claim 4, wherein said outer bag and saidinner bag are heat welded together, thereby creating a seal binding saidouter bag to said inner bag, and also binding opposed sides of saidinner bag together in said seam.
 9. The airbag cushion set forth inclaim 4, wherein said outer bag and said inner bag are adhesively bondedtogether, thereby creating a seal binding said outer bag to said innerbag, and also binding said opposed sides of said inner bag together insaid seam.
 10. The airbag cushion set forth in claim 4, wherein saidouter bag and said inner bag are further attached together by means of asewn seam provided along said heat welded seam.
 11. A method formanufacturing an airbag cushion, said method comprising the steps of:providing a first substrate to serve as an inner layer of an airbagcushion; providing a second substrate to serve as an outer layer of anairbag cushion; arranging said first and second substrates in a stackedconfiguration; and attaching said first and second substrates togetherto form said airbag cushion.
 12. The method set forth in claim 11,wherein said first substrate is selected from the group consisting of:polyolefin, urethane, polyurethane, polyester, polyamides, and anycombinations thereof.
 13. The method set forth in claim 11, wherein saidsecond substrate is made of material selected from the group consistingof: polyester, nylon, and any combinations thereof.
 14. The method setforth in claim 11, wherein said second substrate is selected from thegroup consisting of: woven fabric, non-woven, weft insertion, film andany combinations thereof.
 15. The method set forth in claim 11, whereinsaid substrates are attached together simultaneously using heat welding.16. The method set forth in claim 15, wherein said substrates arefurther attached together by providing a sewn seam within or directlyadjacent to said heat weld.
 17. A method for manufacturing a two-layerairbag cushion, said method comprising the steps of: providing an innerlayer of material to impart low air permeability characteristics to saidairbag cushion, said inner layer formed into a desired shape having apocket for receiving and retaining gas under pressure; providing anouter layer of material to enhance strength characteristics of saidairbag cushion; and disposing said inner layer within said outer layer,and enclosing said outer layer about said inner layer.
 18. The methodset forth in claim 17, further including the step of sewing an outerperimeter of said outer layer together so that said perimeter seam doesnot include or penetrate said inner layer.
 19. The method set forth inclaim 17, further including the step of forming chambers on an interiorportion of said inner layer.
 20. The method set forth in claim 19,including the step of using heat welds to form said chambers.
 21. Themethod set forth in claim 20, including the step of sewing said outerlayer to said inner layer within or adjacent to said heat welds formingsaid chambers.